AUTONOMOUS NAVIGATION
|  Current Navigation
|  Future Navigation
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Throughout the primary mission, about once per week, AutoNav was invoked by the operating sequence to allow it to acquire optical navigation images. It turned the spacecraft and the integrated camera and imaging spectrometer to take pictures of asteroids and stars, analyzing them itself to determine its location. The apparent position of an asteroid relative to the much more distant stars allowed AutoNav to calculate where it was in the vast solar system. This was the first time a spacecraft had accomplished such a feat. All other spacecraft are told where they are by engineers analyzing data from the spacecraft, including its radio signal. This sophisticated system commanded the ion propulsion system to pressurize its xenon tanks for thrusting, and commanded the spacecraft's attitude control system to turn the spacecraft to thrust in the direction AutoNav desired. AutoNav also determined how much power to devote to the ion propulsion system, which used electricity to ionize and accelerate xenon. To do this, AutoNav had knowledge of how much power the advanced solar arrays could produce and how much power the spacecraft consumed apart from the ion propulsion system. The solar arrays generated less power as the spacecraft receded from the Sun, and the spacecraft consumed more power as it ventured farther from the hot Sun because it needed to operate its heaters more. But AutoNav knew how far the spacecraft was from the Sun, so it calculated how much power was available for the ion propulsion system. Combining a knowledge of how much thrusting has been accomplished, the gravitational forces of the Sun and planets, and other information, AutoNav calculated where the spacecraft was headed. If it was not on course, then AutoNav determined how to change the upcoming direction in which it pointed the ion thruster and the duration of thrusting to assure that it reached the target its human colleagues had given it. AutoNav operated extremely well, demonstrating another powerful capability in DS1's set of advanced technologies.
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